| In recent years, global navigation satellite system (GNSS) signals have been studied as opportunistic bistatic radar transmissions. Most of the previous work has concentrated on bistatic radar using Global Positioning System (CPS) signals to remotely sense Earth surface characteristics, such as ocean surface roughness and heights. This dissertation extends this field and investigates remote sensing using GNSS bistatic radar as applied to land surfaces. Two applications of GNSS bistatic radar, soil moisture remote sensing and aircraft altimetry, are studied in detail. Characteristics of land surface remote sensing are addressed, including the bistatic geometry, signal scattering, georeferencing with respect to terrain models, fading characteristics, and parameter estimation.; Numerous experimental campaigns were conducted over varied terrain using aircraft and tower platforms. These data were analyzed to investigate sensitivity to soil moisture, both spatially and temporally, and in the presence of surface roughness. They were also compared with coincident measurements from a radiometer instrument. The results indicate that the CPS bistatic radar technique is effective in mapping the spatial and temporal characteristics of soil moisture and correlated well with other instruments and in situ measurements. The distinguishing feature of the GNSS bistatic radar measurement with respect to radiometers and monostatic radars is the bistatic radar sensitivity to small surface features due to a small footprint and its relative insensitivity to roughness.; Heights above the terrain and sea surface are also estimated from experimental data and compare well with elevation models and measurements from commercial radar altimeters. The results indicate that GNSS bistatic radar provides a means to perform aircraft altimetry in favorable scattering conditions with an optimized receiver. This type of instrument is inexpensive relative to stand-alone radar altimeters for personal and commercial aviation users who already use GNSS systems for navigation. Additionally, the GNSS bistatic radar provides a non-transmitting altimeter capability for stealth applications. |
